Interfacing Stepper Motor with 8051 Microcontroller

The Stepper motor is a brushless motor and the total number of steps are divided into steps. There are many applications for the stepper motor in the field of robotics and Mechatronics. The angle of the step is called as the stepper angle and there are two types of stepper motors, they are discussed in the article. The most common used stepper motor in the electronic hobbyists is the unipolar stepper motor. In this article, we have discussed briefly the interfacing stepper motor with the 8051 microcontroller. In this, the integrated circuit is AT89C51 which is from the microcontroller family.

What is a Stepper Motor?

A stepper motor is a brushless DC electric motor. It divides the full rotation into the equal no. of steps. Without any feedback sensor the position of the motor is moved and hold on one of these steps. The applications of motors are in respect to the torque and speed. The switched reluctance motors are large stepping motors with the help of the reduced pole count and they are generally closed loop. Stepper motors are also known as the step motor or stepping motors.

Stepper Motor

Different Types of Stepper Motors

The stepper motors are mainly divided into three types which are following

Permanent magnet stepper

Hybrid synchronous stepper

Variable reluctance stepper

Two Phase Stepper Motor

The two-phase stepper motor has two basic winding arrangements with the electromagnetic coil are unipolar and bipolar.

Unipolar Stepper Motor

From the word of unipolar the “uni” means the current flow in one direction and this motor has two winding per phase, for each direction of the magnetic field. The following diagram shows the unipolar stepper motor.

Unipolar Stepper Motor

The unipolar stepper motors are used in three modes of operations which are wave drive, full drive, and a half drive. The description of each drive is described below and it has its own advantages and disadvantages thus we can choose the required drive according to the application.

Unipolar Stepper Motor Winding

Wave Drive

In the wave drive mode, there is only once electromagnetic is eager at a time. The generated force will be less when it is compared with the full drive in which the electromagnets are eager at the time and however the power consumption is important the torque. The wave drives are used rarely and the sequence of the wave drive stepping is following

Steps

A

B

C

D

1

1

0

0

0

2

0

1

0

0

3

0

0

1

0

4

0

0

0

1

Full Drive

In the full drive modes, there are two electromagnets are energized at one time, hence the torque generated is more when it is compared with the wave drive. The power consumption of full drive is higher than the other modes. The sequence of full drive stepper motor is shown in the following table.

Steps

A

B

C

D

1

1

1

0

0

2

0

1

1

0

3

0

0

1

1

4

1

0

0

1

Half Drive

The half drive is a combination of both drives which are wave drive and full drive. In the half drive mode, there is one and two electromagnets are energized. The half drive mode is used commonly to increase the angular resolution of the motor except the force will be less around the 70% at the half step position. When we use the half drives we can observe the angular resolution double. The sequence of the half drive stepping is shown in the following table.

Steps

A

B

C

D

1

1

0

0

0

2

1

1

0

0

3

0

1

0

0

4

0

1

1

0

5

0

0

1

0

6

0

0

1

1

7

0

0

0

1

8

1

0

0

1

Bipolar Stepper Motor

The bipolar stepper motor has a single winding per phase. From the word of bipolar the Bi means the current in the winding to reverse a magnetic pole, thus the driving circuit is complicated, typically with an H-bridge arrangement. The following diagram shows the bipolar stepper motor.

Bipolar Stepper Motor

Stepper Motor Working

The working principle of the stepper motor is electromagnetic. The construction of the stepper motor is shown in the following figure. It consists of the rotor which is a permanent magnet and a stator with electromagnets. Currently, if we give power supply to the stator’s winding there will be a development of the magnetic field in the stator. With the help of the permanent magnet, the rotor of the motor is made. This is the basic working principle of the stepper motor.

Stepper Motor Working

Circuit Diagram of Stepper Motor

The following circuit diagram shows the four-stage stepper motor circuit and it is similar to the two-stage stepper motor. By observing the circuit diagram the reset pin is connected to the transistor Q2 and opened transistors are Q2, Q3 pins are connected to the other two transistors to generate the four pulses driving and to run the four stage stepper motor. Therefore, it is clear that we can make up to ten stage stepper motor. The diodes are connected to the collector terminal of the NPN transistor and the diodes are used to protect the transistors from the inductance spiking of the stepper motor. If the diodes are not placed there may be a risk to glow the transistors.

Circuit Diagram of Stepper Motor

The diodes are connected to the collector terminal of the NPN transistor and the diodes are used to protect the transistors from the inductance spiking of the stepper motor. If the diodes are not placed there may be a risk to glow the transistors.

Interfacing Stepper Motor with the 8051

The components of stepper motor interfacing with the 8051 microcontrollers are an AT89C51 microcontroller, ULN2003A motor, resistor, capacitor, Crystal oscillator. The AT89C51 is a low power, high performance, 8bit COMS and it is from the 8051 microcontroller family. The microcontroller has 32 programmable I/O lines and it also has the 4K bytes of flash programmable and erasable memory. The crystal oscillator is connected externally to the 18 and 19 pins of the microcontroller. The stepper motor is connected to the port2 of the microcontroller with the help of the driver IC.

Interfacing Stepper Motor with the 8051

The ULN2003A is used to force the current of the stepper motor and it requires more than the 60mA of current. It is a current driver integrated circuit and it consists of the seven pairs of Darlington arrays with the common emitter. The total no. of IC pins are 16 in which 7 pins are input pins, other 7 pins are out pins and remaining two pins are connected to the ground and Vcc. The first four pins of ULN2003A are connected to the microcontroller and the output pins are connected to the stepper motor.

The stepper motor consists of 6 pins in this the two pins are connected to the power supply with 12V and remaining four pins are connected to the output of the stepper motor. By the given step angle the stepper motor will rotate, each rotation of step has a fraction of the full cycle and it depends on the mechanical parts and the driving method.

The stepper motor has the stator and rotor. The rotors have the stable magnet and the stator has the coil. The basic structure of a this motor has the 4 coils with the 90 degrees rotation and the four coils are in the cyclic order. There are different methods like full drive, half drive and wave drive is described starting with the article.

Advantages of the Stepper Motor

The consumption of power is less

The stepper motor requires low operating voltage

Applications of the Stepper Motor

It is also used in the mechanical applications. The stepper motors are also used in the disk drives, matrix printers and etc.,

This article describes the interfacing stepper motor with the 8051 microcontroller. I hope by reading this article you have got some basic knowledge about the stepper motor interfacing with the microcontroller. If have any queries about this article or about the interfacing microcontroller with the liquid crystal diode projects, please feel free to comment in the below section. Here is the question for you, What are the functions of the stepper motor?